Congrats on making it that far! That's farther than most developers ;)
I have no idea how to get 6500 prosperity in an era, but people have been suggesting some pretty great builds on this board, so look around. For example: viewtopic.php?f=12&t=683

For the 600 prosperity in 30 minutes, it's mostly important to play very fast. Make sure all giants are moving at all times. This probably includes pausing to plan. Play the challenges that villages pose you. The disadvantage of a fixed build, is that you sometimes have to ignore certain challenges, while fulfilling every challenge is the only way to get to 16 ambassadors fast.